Layered clay intercalates and exfoliates having a low quartz content

ABSTRACT

The invention is directed to a polymer-clay nanocomposite material comprising a melt-processible matrix polymer and a layered clay material having low quartz content. This invention is also directed to a process for preparing a polymer-clay nanocomposites, and articles or products produced from nanocomposite materials.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.09/583,120 filed May 30, 2000.

FIELD OF THE INVENTION

The present invention relates generally to polymer-clay nanocompositescomprising a matrix polymer and a layered clay material. Thepolymer-clay nanocomposites comprising the layered clay material may beprocessed under normal conditions while achieving low haze and improvedoxygen barrier properties. This invention further relates to articlesproduced from the polymer-clay nanocomposites and processes relating tothe nanocomposites.

BACKGROUND OF THE INVENTION

Thermoplastic materials are being increasingly used in the packaging ofbeverages and perishable foods. Plastics are often the material ofchoice for food and beverage packaging because of their clarity,flexibility, toughness, high gas barrier, lighter weight, processabilityand high gloss.

Polymer composites comprising a layered clay material having plateletparticles have potential for improved properties, including increasedgas barrier, heat deflection temperature, and modulus. However, it hasbeen found that films and articles made from polymer-clay nanocompositesoften exhibit increased haze. The origin of this haze is not definitive,but platelet-particle agglomerates, impurities in the clay, crystallinehaze, surface inhomogeniety all may contribute to increased haze. Theimpurities associated with montmorillonite clay, such as quartz, can notbe modified to be compatible with the nylon resin molecules. Upon blowmolding of the nanocomposite materials in the container fabricatingprocess, voids will be generated around the inorganic particles. Thevoids may contribute to the haze. Furthermore, processes that include ahigh degree of orientation, or stretching of a material, often lead tothe presence of voids and increased haze. For applications where clarityis important, such as beverage packaging, including beer packaging,films, etc., presence of voids and haze hinders aesthetic appeal andalso may significantly affect physical properties of interest, such asgas barrier.

The presence of voids and haze in structures, particularly orientedstructures containing polymer-clay composites make such structures lessapplicable for aesthetic and functional reasons. It is desirable,therefore, to significantly reduce the haze/voids of articles made frompolymer-clay platelet particle nanocomposites.

Thus, there remains a need for polymer-clay nanocomposites that resultin reduced haze and voids in articles made from such nanocomposites.There is also a need for articles and structures, particularly orientedmonolayer and/or multilayer structures, comprising the nanocompositematerial.

SUMMARY OF THE INVENTION

The present invention is generally related to polymer-claynanocomposites. The nanocomposites of this invention result in anacceptable and reduced level of haze and voids, and improved physicalproperties afforded by the incorporation therein of a layered claymaterial comprising platelet particles. The reduced level of haze andvoids are achieved by reducing the quartz content in the layered claymaterial.

As embodied and broadly described herein, this invention, in oneembodiment, relates to a polymer-clay nanocomposite comprising a meltprocessible matrix polymer and a layered clay material having less thanabout 2.0% by weight of quartz, based on the weight of the claymaterial.

In another embodiment, the present invention relates to a multi-layerarticle having low haze comprising: (a) at least two structural polymerlayers preferably comprising poly(ethylene terephthalate) (PET), or acopolymer thereof; and (b) at least one barrier layer disposed betweenthe at least two structural layers comprising a melt processible matrixpolyamide and incorporated therein a layered clay material having lessthan about 2.0% by weight of quartz, based on the weight of the claymaterial.

In yet another embodiment, the present invention relates to a processfor preparing a polymer-clay nanocomposite comprising the steps of: (i)forming a concentrate comprising an oligomeric resin and a layered claymaterial having less than about 2.0% by weight of quartz, based on theweight of the clay material; and (ii) melt mixing the concentrate with amelt processible matrix polymer to form a polymer-clay nanocomposite.

In yet another embodiment, the present invention relates to a processfor reducing haze in an article having a nanocomposite materialcomprising: (i) preparing a polymer-clay nanocomposite comprising thestep of melt mixing a melt processible matrix polymer and a layered claymaterial having less than about 2.0% by weight of quartz, based on theweight of the clay material, to form a polymer-clay nanocomposite; and(ii) molding an article from the nanocomposite material, wherein thearticle has a haze which is at least about 4 percent lower than that ofan article formed from a nanocomposite having unpurified clay therein.

Additional advantages of the invention will be set forth in part in thedetailed description, including the figures, which follows, and in partwill be obvious from the description, or may be learned by practice ofthe invention. The advantages of the invention will be realized andattained by means of the elements and combinations particularly pointedout in the appended claims. It is to be understood that both theforegoing general description and the following detailed description areexemplary and explanatory of preferred embodiments of the invention, andare not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is flow chart illustrating one embodiment of the steps of a knownprocess for clay purification and cation exchange.

FIG. 2 is an optical photograph at 100× magnification of an article walllayer produced from the nanocomposite of Example 3.

FIG. 3 is an optical photograph at 100× magnification of an article walllayer produced from the nanocomposite of the Comparative Example 3.

FIG. 4A is an optical photograph at 400× magnification of a trilayerfilm before biaxially stretching having a middle layer produced from thenanocomposite of the Comparative Example 3.

FIG. 4B is an optical photograph at 400× magnification of a trilayerfilm before biaxially stretching having a middle layer produced from thenanocomposite of the Comparative Example 3.

FIG. 5A is an optical photograph at 400× magnification (at the locationof FIG. 4A) of the trilayer film after biaxially stretching.

FIG. 5B is an optical photograph at 400× magnification (at the locationof FIG. 4B) of the trilayer film after biaxially stretching.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to thefollowing detailed description of the invention and the examplesprovided therein. It is to be understood that this invention is notlimited to the specific components, articles, processes and/orconditions described, as these may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. For example,reference to an “article,” “container” or “bottle” prepared from thenanocomposites and processes of this invention is intended to include aplurality of articles, containers or bottles.

Ranges may be expressed herein as from “about” or “approximately” oneparticular value and/or to “about” or “approximately” another particularvalue. When such a range is expressed, another embodiment includes fromthe one particular value and/or to the other particular value.Similarly, when values are expressed as approximations, by use of theantecedent “about,” it will be understood that the particular valueforms another embodiment.

Whenever used in this specification, the terms set forth shall have thefollowing meanings:

“Layered clay material,” “layered clay,” “layered material,” “claymaterial” or “clay” shall mean any organic or inorganic material ormixtures thereof, such as a smectite clay mineral, which is in the formof a plurality of adjacent, bound layers. The layered clay comprisesplatelet particles and is typically swellable.

“Platelets,” “platelet particles” or “particles” shall mean individualor aggregate unbound layers of the layered clay material. These layersmay be in the form of individual platelet particles, ordered ordisordered small aggregates of platelet particles (tactoids), and/orsmall aggregates of tactoids.

“Dispersion” or “dispersed” is a general term that refers to a varietyof levels or degrees of separation of the platelet particles. The higherlevels of dispersion include, but are not limited to “intercalated” and“exfoliated.”

“Intercalated” or “intercalate” shall mean a layered clay material thatincludes treated or organically modified layered clay material having anincrease in the interlayer spacing between adjacent platelets particlesand/or tactoids. The intercalate may also refer to an “organoclay.”

“Exfoliate” or “exfoliated” shall mean platelets dispersed mostly in anindividual state throughout a carrier material, such as a matrixpolymer. Typically, “exfoliated” is used to denote the highest degree ofseparation of platelet particles.

“Exfoliation” shall mean a process for forming an exfoliate from anintercalated or otherwise less dispersed state of separation.

“Nanocomposite” shall mean a polymer and/or copolymer having dispersedtherein a plurality of individual platelets obtained from a layered claymaterial.

“Matrix polymer” shall mean a thermoplastic or thermosetting polymer inwhich the clay material is dispersed to form a nanocomposite.

The present invention relates to polymer-clay composites that haveimproved physical properties afforded by the incorporation of clayplatelet particles and produce acceptable reduced haze levels fordesired applications.

As described above, clay platelet particles in a polymer nanocompositemay induce crystallization, haze and void formation. Without being boundby any particular theory, it is believed that the polymer-claynanocomposite on processing, such as stretching or orientation of thefilms, leads to very high levels of haze due to voids and/or fromcrystallization of the matrix polymer around the dispersed clayparticles which renders the polymer nanocomposites less desirable forfood packaging applications, for example. This stretch blow moldingphenomena can even lead to void and hole formation in the polymer films,which minimizes the usefulness of these compositions in barrierapplications.

In one embodiment, we have discovered that using a naturally pure clayand/or a clay purified through a purification process, whereby severalimpurities including quartz that cause haze and voids are selectivelyremoved from clay, results in novel polymer-clay composite compositionsthat result in reduced haze and voids (as seen by optical microscopy),as compared to previous polymer-clay platelet particle composites.

The polymer-clay nanocomposite of the present invention having thereinthe purified or clean low quartz clay has improved barrier to gas whenformed into a wall or article compared to a neat polymer formed into thesame or similar structure. In addition, these nanocomposites have beenfound to show unexpected resistance to haze formation, crystallization,void formation and other defect formation in the presence of dispersedand/or exfoliated pure and/or purified clays when undergoing orientationand/or other film or article processing steps.

For comparison, a typical clay purification process is shown in FIG. 1.In step 1, bentonite clay is mined from selected sites (reservoir). Instep 2, bentonite clay is refined to produce montmorillonite-type clay.In step 3, the cation-exchange process takes place whereby the sodiumion associated with the montmorillonite is exchanged with an appropriatecation. This step requires exchange reaction time, washing, drying, andpossibly grinding. The resulting organoclays produced according to priorprocesses have been used to produce polymer-platelet compositions inmany applications.

The quartz content of a clay material can be quantified by comparing thediffraction peak intensity of the quartz powder X-ray diffractionpatterns. The intensity of the diffraction peak has a linearrelationship with the quartz content. A calibration curve can begenerated with a series known quartz content samples. The calibrationpeak can be used is at 3.35 Å. In general, the linear regression of thecalibration curves is in the range of 0.90 to 0.999. The calibrationcurve can also be generated with the ratios of the quartz peak (3.35 Å)to the intrinsic clay (e.g., montmorillonite) diffraction peak at (1.50Å, d060) and the known quartz content in the standard samples. The latercalibration curve can eliminate the possible X-ray sample preparationerrors.

Low quartz clay (e.g., montmorillonite) can be obtained from miningselections, as well as clay purification processes. In general, for agiven clay deposit, modified processing conditions, such as highercentrifugation speed, lower slurry solid content can generate lowerquartz clay. The quartz morphology and content remains essentiallyunchanged in the onium ion modification process.

An improved clay purification process useful in the present inventionresults in clay platelet particles having a low quartz content. Thecleaned or purified clay is used in forming the polymer-claynanocomposite. According to one embodiment of this invention, bentonite,montmorillonite and other clays can be purified through a seriespurification process having individual steps, as detailed in U.S. Pat.No. 6,050,509, issued Apr. 18, 2000, the entirety of which is herebyincorporated by reference. The individual steps can be used once orrepeated.

In summary, according to one embodiment of the U.S. Pat. No. 6,050,509,montmorillonite clay, for example, is dispersed in water at about 6-10wt % concentration to form a clay slurry. The clay slurry is passedthrough a series of hydrocyclones to remove larger particles(impurities) while retaining clay particles having a size of about 100microns, or less. The clay may be exchanged to 95% Na-form in an ionexchange column and centrifuged. The final purified montmorillonite clayshould have particle size less than 10 micron. By varying the slurryconcentration, flow rate through the hydrocyclone, and speed of thecentrifuge, low quartz clays have been achieved.

Quartz content can be determined by powder X-ray diffraction methodbased on the relative intensity of quartz diffraction peak at 3.34 Å.Lower quartz montmorillonite has been defined for a clay with less thanabout 2.0 wt %, preferably less than about 1.5 wt % quartz, morepreferably less than 1.0 wt % quartz, based on the weight of the claymaterial.

In addition to the removal of various impurities present in the clay bythe cleaning or purifying process described in U.S. Pat. No. 6,050,509,according to the present invention, further impurities are selectivelyremoved from the clay material by incorporating a cryogenic magneticseparation step in refining the layered clay thereby producing asuper-clean clay material. For example, the cryogenic magneticseparation step is a common way to remove iron oxides, such as hematite.The paramagnetic species will move to the magnet surface and leave theclay system. This step may be used from the beginning, but it is moreeffective to use at the end of a purification process. Moreover, thecryogenic magnetic separation step can, at the least, remove quartzparticles (SiO₂) present in the unrefined clay.

Quartz particles have been identified as a cause of voids in orientedfilms containing polymer-clay nanocomposites where the step of cryogenicmagnetic separation is not used to refine the clay material. However,low quartz clay particles may also be achieved without a cryogenicmagnetic separation step.

Although this invention is generally directed to pure or purified clays,preferably, a clay processed according to the present invention and/orused in the present invention has less than about 2.0% by weight,preferably less than about 1.5% by weight, more preferably less thanabout 1.0% by weight, even more preferably less than about 0.7% byweight and most preferably less than about 0.5% by weight of quartzparticles, based on the weight of the pure or purified clay material.

Some iron oxides are also presented in the initial ores and they mayadhere to the sides of montmorillonite clay. Strong magnet fields can beused to separate these iron oxide particles and the iron oxide particlesadhered to the montmorillonite clays. The more preferred magnet used inthis type of process is a cryogenic superconductor magnet.

The magnet may be a permanent magnet, an electric-induced magnet, or thelike. The power levels of the magnet determine the efficiency of theseparation process. The resulting purified montmorillonite clays can bedried and milled.

In a particular embodiment, regular clay (e.g., montmorillonite clay) isdispersed into de-ionized water at about 4 wt %. The slurry is sentthrough a magnetic field range from about 0.8 to about 3 Tesla, at aconstant speed, e.g., about 10 gal/min. The magnet field can begenerated from permanent magnet or cryogenic magnet. The magneticallypurified montmorillonite clay has about 100 wt % of its original ionoxides removed, such as hematite as evidenced from XRD and XRF analysisresults.

Thereafter, an organic cation is used to exchange the cations of theclay. For example, about 115% octadecyl ammonium chloride, based on thecation exchange capacity of the montmorillonite clay, may be used tomodify the clay surface. The exchange reaction time is about 4 hrs,compared with approximately 1-2 hrs, regular reaction time to ensurecomplete exchange. The exchanged organoclay is de-watered throughfiltration. The filter cake is about 20 wt % solid. The filter cake iswashed with hot de-ionized water twice. The filter cake is broken intosmall chunks less than about 0.5 cm, and dried in vented air for twodays. The final organoclay is dried in a 50° C. oven for about 4 hr.before fine grinding to reduce particle size. For generalorgano-montmorillonite clay production, the drying temperature is about90 to about 120° C. overnight before milling.

The resulting purified and organically-modified organo-montmorilloniteclay (S-ODA-PGW) has a much brighter color than the regular claymaterials (PGW-ODA), as the color parameters shows in the followingTable 1.

TABLE 1 Sample Brightness L* A* b* S-ODA-PGW 86 96.83 0.50 4.55 PGW-ODA68 90.45 2.61 7.34

Furthermore, we have discovered that the cation-exchange process may beimproved by providing the longer reaction times to allow completeexchange of the cations, to remove sodium chloride and other impuritiespresent. Moreover, the gentle, low temperature drying conditions, andreduced particle size lead to a further improved organoclay.

This invention also relates to improved montmorillonite clay having alow quartz content and an organoclay that displays improved clarity andphysical properties and a process for producing the improved organoclay.Another embodiment of the present invention relates to apolymer-platelet nanocomposite containing an organoclay of the presentinvention that displays low haze/voids upon orienting and/or stretching.

In one aspect, this invention relates to a low quartz polyamide-claynanocomposite material comprising a polyamide having dispersed thereinplatelet particles derived from various clay materials that are pureand/or are purified, and may be untreated or metal intercalated,organically modified through cation exchange, or intercalated with otherhigh molecular weight pretreatment compounds. Any polyamide may be usedin the process of this invention. The polyamide nanocomposite ispreferably a poly(m-xylylene adipamide) polymer or copolymernanocomposite having an I.V. of at least about 0.3 dL/g, preferably atleast about 0.7 dL/g.

In another aspect, this invention relates to a low quartz polyester-claynanocomposite material comprising a polyester having dispersed thereinplatelet particles derived from various clay materials that are pureand/or purified, and may be untreated, metal intercalated, organicallymodified through cation exchange, or intercalated with other highmolecular weight pretreatment compounds. The polyester nanocomposite ispreferably a polyethylene terephthalate polymer or copolymernanocomposite having an I.V. of at least about 0.3 dL/g, preferably atleast about 0.5 dL/g.

The polymer-clay nanocomposite of this invention comprises a polymer andup to about 25 weight percent of swellable layered clay material, whichis pure and/or purified according to a process of this invention and mayin turn be intercalated (organically modified) with an organic cation,preferably an onium ion. The pure and/or purified clay material has alow quartz content and comprises platelet particles, which are dispersedin the matrix polymer.

If desired, other clay treatments may be present during or prior to theformation of the composite by melt mixing for the purposes of aidingexfoliation of the treated or untreated swellable layered particles intothe polymer.

Formation of a polymer-clay nanocomposite may be achieved by severaldifferent methods. For polyamides, formation of a polyamide-claynanocomposite includes, but is not limited to, reactive chain extensionof an oligomeric polyamide-platelet particle composite, and meltcompounding of an oligomeric polyamide composite with a high molecularweight, melt processible polyamide. The monomer unit of the meltprocessible polyamide may be the same as or different than theoligomeric polyamide.

Processes for forming polyester-clay nanocomposites include, but are notlimited to solid state polymerization, melt compounding with meltprocessible polyester, and/or their combinations. In one embodiment ofthis invention, the I.V. of an oligomeric polyester-clay composite isincreased by solid state polymerization. In another embodiment of thisinvention, an oligomeric polyester-clay composite is compounded with amelt processible polyester and used as is, or is increased in I.V. bysolid state polymerization. The monomer unit of the melt processiblepolyester may be the same as or different than the oligomeric polyester.

Polymers

Any melt-processible polymer or oligomer may be used in this invention.Illustrative of melt-processible polymers are polyesters,polyetheresters, polyamides, polyesteramides, polyurethanes, polyimides,polyetherimides, polyureas, polyamideimides, polyphenyleneoxides,phenoxy resins, epoxy resins, polyolefins, polyacrylates, polystyrenes,polyethylene-co-vinyl alcohols (EVOH), and the like or theircombinations and blends. Although the preferred polymers are linear ornearly linear, polymers with other architectures, including branched,star, cross-linked and dendritic structures may be used if desired.

The preferred polymers include those materials that are suitable for usein the formation of monolayer and/or multilayer structures withpolyesters and can be oriented, and include polyesters, polyamides,polyethylene-co-vinyl alcohols (such as EVOH), and similar or relatedpolymers and/or copolymers. The preferred polyester is poly(ethyleneterephthalate) (PET), or a copolymer thereof. The preferred polyamide ispoly(m-xylylene adipamide) or a copolymer thereof.

Suitable polyesters include at least one dibasic acid and at least oneglycol. A polyester of this invention may comprises the polycondensationpolymerization reaction product (or residue) of the glycol component andthe dicarboxylic acid component. “Residue,” when used in reference tothe components of the polyester of this invention, refers to the moietythat is the resulting product of the chemical species in a particularreaction scheme, or subsequent formulation or chemical product,regardless of whether the moiety is actually obtained from the chemicalspecies.

The primary dibasic acids are terephthalic, isophthalic,naphthalenedicarboxylic, 1,4-cyclohexanedicarboxylic acid and the like.The various isomers of naphthalenedicarboxylic acid or mixtures ofisomers may be used, but the 1,4-, 1,5, 2,6-, and 2,7-isomers arepreferred. The 1,4-cyclohexanedicarboxylic acid may be in the form ofcis, trans, or cis/trans mixtures. In addition to the acid forms, thelower alkyl esters or acid chlorides may be also be used.

A polyester of this invention may be prepared from one or more of thefollowing dicarboxylic acids and one or more of the following glycols.

The dicarboxylic acid component of the polyester may optionally bemodified with up to about 50 mole percent of one or more differentdicarboxylic acids. Such additional dicarboxylic acids includedicarboxylic acids having from 6 to about 40 carbon atoms, and morepreferably dicarboxylic acids selected from aromatic dicarboxylic acidspreferably having 8 to 14 carbon atoms, aliphatic dicarboxylic acidspreferably having 4 to 12 carbon atoms, or cycloaliphatic dicarboxylicacids preferably having 8 to 12 carbon atoms. Examples of suitabledicarboxylic acids include phthalic acid, isophthalic acid, terephthalicacid, naphthalene-2,6-dicarboxylic acid, cyclohexanedicarboxylic acid,cyclohexanediacetic acid, diphenyl-4,4′-dicarboxylic acid,phenylenedi(oxyacetic acid), succinic acid, glutaric acid, adipic acid,azelaic acid, sebacic acid, and the like. Polyesters may also beprepared from one or more of the above dicarboxylic acids.

Typical glycols used in the polyester include those containing from twoto about ten carbon atoms. Preferred glycols include ethylene glycol,propanediol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol,diethylene glycol and the like. The glycol component may optionally bemodified with up to about 50 mole percent, preferably up to about 25mole percent, and more preferably up to about 15 mole percent of one ormore different diols. Such additional diols include cycloaliphatic diolspreferably having 6 to 20 carbon atoms or aliphatic diols preferablyhaving 3 to 20 carbon atoms. Examples of such diols include: diethyleneglycol, triethylene glycol, 1,4-cyclohexanedimethanol, propane-1,3-diol,butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol,3-methylpentanediol-(2,4), 2-methylpentanediol-(1,4),2,2,4-trimethylpentane-diol-(1,3), 2-ethylhexanediol-(1,3),2,2-diethylpropane-diol-(1,3), hexanediol-(1,3),1,4-di-(2-hydroxyethoxy)-benzene, 2,2-bis-(4-hydroxycyclohexyl)-propane,2,4-dihydroxy-1,1,3,3-tetramethyl-cyclobutane,2,2-bis-(3-hydroxyethoxyphenyl)-propane,2,2-bis-(4-hydroxypropoxyphenyl)-propane and the like. Polyesters mayalso be prepared from one or more of the above diols.

Small amounts of multifunctional polyols such as trimethylolpropane,pentaerythritol, glycerol and the like may be used, if desired. Whenusing 1,4-cyclohexanedimethanol, it may be the cis, trans or cis/transmixtures. When using phenylenedi(oxyacetic acid), it may be used as 1,2;1,3; 1,4 isomers, or mixtures thereof.

The polymer may also contain small amounts of trifunctional ortetrafunctional comonomers to provide controlled branching in thepolymers. Such comonomers include trimellitic anhydride,trimethylolpropane, pyromellitic dianhydride, pentaerythritol,trimellitic acid, trimellitic acid, pyromellitic acid and otherpolyester forming polyacids or polyols generally known in the art.

The polyesters of the present invention exhibit an I.V. of about 0.25 toabout 1.5 dL/g, preferably about 0.4 to about 1.2 dL/g, and morepreferably of about 0.7 to about 0.9 dL/g. The I.V. is measured at 25°C. in a 60/40 by weight mixture in phenol/tetrachloroethane at aconcentration of 0.5 grams per 100 ml. Polyesters having an I.V. withinthe ranges specified above are of sufficiently high molecular weight tobe used in the formation of the articles of the present invention.

Suitable polyamides include partially aromatic polyamides, aliphaticpolyamides, wholly aromatic polyamides and/or mixtures thereof. By“partially aromatic polyamide,” it is meant that the amide linkage ofthe partially aromatic polyamide contains at least one aromatic ring anda nonaromatic species. Suitable polyamides have an article formingmolecular weight and preferably an I.V. of greater than 0.4.

Preferred wholly aromatic polyamides comprise in the molecule chain atleast 70 mole % of structural units derived from m-xylylene diamine or axylylene diamine mixture comprising m-xylylene diamine and up to 30% ofp-xylylene diamine and an aliphatic dicarboxylic acid having 6 to 10carbon atoms, which are further described in Japanese PatentPublications No. 1156/75, No. 5751/75, No. 5735/75 and No. 10196/75 andJapanese Patent Application Laid-Open Specification No. 29697/75.

Polyamides formed from isophthalic acid, terephthalic acid,cyclohexanedicarboxylic acid, meta-orpara-xylylene diamine, 1,3- or1,4-cyclohexane(bis)methylamine, aliphatic diacids with 6 to 12 carbonatoms, aliphatic amino acids or lactams with 6 to 12 carbon atoms,aliphatic diamines with 4 to 12 carbon atoms, and other generally knownpolyamide forming diacids and diamines can be used. The low molecularweight polyamides may also contain small amounts of trifunctional ortetrafunctional comonomers such as trimellitic anhydride, pyromelliticdianhydride, or other polyamide forming polyacids and polyamines knownin the art.

Preferred partially aromatic polyamides include, but are not limited topoly(m-xylylene adipamide), poly(m-xylyleneadipamide-co-isophthalamide), poly(hexamethylene isophthalamide),poly(hexamethylene isophthalamide-co-terephthalamide),poly(hexamethylene adipamide-co-isophthalamide), poly(hexamethyleneadipamide-co-terephthalamide), poly(hexamethyleneisophthalamide-co-terephthalamide) and the like or mixtures thereof.More preferred partially aromatic polyamides include, but are notlimited to poly(m-xylylene adipamide), poly(hexamethyleneisophthalamide-co-terephthalamide), poly(m-xylyleneadipamide-co-isophthalamide), and/or mixtures thereof. The mostpreferred partially aromatic polyamide is poly(m-xylylene adipamide).

Preferred aliphatic polyamides include, but are not limited topoly(hexamethylene adipamide) and poly(caprolactam). The most preferredaliphatic polyamide is poly(hexamethylene adipamide). Partially aromaticpolyamides are preferred over the aliphatic polyamides where goodthermal properties are crucial.

Preferred aliphatic polyamides include, but are not limited topolycapramide (nylon 6), poly-aminoheptanoic acid (nylon 7),poly-aminonanoic acid (nylon 9), polyundecane-amide (nylon 11),polyaurylactam (nylon 12), poly(ethylene-adipamide) (nylon 2,6),poly(tetramethylene-adipamide) (nylon 4,6),poly(hexamethylene-adipamide) (nylon 6,6),poly(hexamethylene-sebacamide) (nylon 6,10),poly(hexamethylene-dodecamide) (nylon 6,12),poly(octamethylene-adipamide) (nylon 8,6), poly(decamethylene-adipamide)(nylon 10,6), poly(dodecamethylene-adipamide) (nylon 12,6) andpoly(dodecamethylene-sebacamide) (nylon 12,8).

The most preferred polyamides include poly(m-xylylene adipamide),polycapramide (nylon 6) and poly(hexamethylene-adipamide) (nylon 6,6).Poly(m-xylylene adipamide) is a preferred polyamide due to itsavailability, high barrier, and processability.

The polyamides are generally prepared by processes which are well knownin the art.

A polyamide of the present invention may comprise the polycondensationpolymerization reaction product (or residue) of a diamine component anda dicarboxylic acid component, and/or those prepared by ring openingpolymerization of lactams. “Residue,” when used in reference to thecomponents of the polyamide of this invention, refers to the moiety thatis the resulting product of the chemical species in a particularreaction scheme, or subsequent formulation or chemical product,regardless of whether the moiety is actually obtained from the chemicalspecies.

The polyamides of the present invention exhibit an I.V. of about 0.25 toabout 1.5 dL/g, preferably about 0.4 to about 1.2 dL/g, and morepreferably of about 0.7 to about 1.0 dL/g. The I.V. is measured at 25°C. in a 60/40 by weight mixture in phenol/tetrachloroethane at aconcentration of 0.5 grams per 100 ml. Polyamides having an I.V. withinthe ranges specified above are of sufficiently high molecular weight tobe used in the formation of the articles of the present invention.

Although not necessarily preferred, the oligomers and/or polymers of thepresent invention may also include suitable additives normally used inpolymers. Such additives may be employed in conventional amounts and maybe added directly to the reaction forming the oligomer or to the matrixpolymer. Illustrative of such additives known in the art include, butare not limited to colorants, pigments, toners, carbon black, glassfibers, fillers, impact modifiers, antioxidants, surface lubricants,denesting agents, UV light absorbing agents, metal deactivators,fillers, nucleating agents, stabilizers, flame retardants, reheat aids,crystallization aids, acetaldehyde reducing compounds, recycling releaseaids, oxygen scavengers, plasticizers, nucleators, mold release agents,compatibilizers, and the like, or their combinations.

All of these additives and many others and their use are known in theart and do not require extensive discussion. Therefore, only a limitednumber will be referred to, it being understood that any of thesecompounds can be used in any combination so long as they do not hinderthe present invention from accomplishing its objects.

The I.V. of an oligomeric polyamide used prior to melt mixing ispreferably from about 0.1 to about 0.5 dL/g, and more preferably fromabout 0.3 dL/g to about 0.5 dL/g, as measured in a mixture of 60 weightpercent phenol and 40 weight percent 1,1,2,2-tetrachloroethane at aconcentration of 0.5 g/100 ml (solvent) at 25° C. Preferably, the I.V.of the high molecular weight matrix polymer is at least about 0.7 dL/gand more preferably is at least about 1.0 dL/g as measured in a mixtureof 60 weight percent phenol and 40 weight percent1,1,2,2-tetrachloroethane at a concentration of 0.5 g/100 ml (solvent)at 25° C. Moreover, the oligomeric polyamide has a number averagemolecular weight of from about 200 to about 10,000 g/mol and may be ahomo or cooligomer.

The I.V. of an oligomeric polyester used prior to melt mixing ispreferably from about 0.05 to about 0.5 dL/g, and more preferably fromabout 0.1 dL/g to about 0.3 dL/g, as measured in a mixture of 60 weightpercent phenol and 40 weight percent 1,1,2,2-tetrachloroethane at aconcentration of 0.5 g/100 ml (solvent) at 25° C. Preferably, the I.V.of the high molecular weight matrix polymer is at least about 0.6 dL/g,and more preferably is about 0.7 dL/g as measured in a mixture of 60weight percent phenol and 40 weight percent 1,1,2,2-tetrachloroethane ata concentration of 0.5 g/100 ml (solvent) at 25° C. Moreover, theoligomeric polyester has a number average molecular weight of from about200 to about 10,000 g/mol and may be a homo or cooligomer.

Clay Material (Platelet Particles)

The nanocomposite compositions of the present invention comprise up toabout 25 weight percent, preferably from about 0.5 to about 20 weightpercent, more preferably from about 0.5 to about 15 weight percent, andmost preferably from about 0.5 to about 10 weight percent of layeredclay material which is pure in that it has a low quartz content or hasbeen purified by any of the processes described herein or by any otherknown process that would purify or eliminate impurities including quartzfrom a clay material. The layered clay material comprises plateletparticles. The amount of platelet particles is determined by measuringthe amount of silicate residue in the ash of the polymer/plateletcomposition when treated in accordance with ASTM D5630-94.

Useful clay materials include natural, synthetic, and modifiedphyllosilicates. Natural clays include smectite clays, such asmontmorillonite, saponite, hectorite, mica, vermiculite, bentonite,nontronite, beidellite, volkonskoite, magadite, kenyaite, and the like.Synthetic clays include synthetic mica, synthetic saponite, synthetichectorite, and the like. Modified clays include fluorinated hectorite,fluorinated mica, and the like. Suitable clays are available fromvarious companies including Nanocor, Inc., Southern Clay Products,Kunimine Industries, Ltd., and Rheox.

Generally, the layered clay materials useful in this invention are anagglomeration of individual platelet particles that are closely stackedtogether like cards, in domains called tactoids. The individual plateletparticles of the clays preferably have thickness of less than about 2 mnand diameter in the range of about 10 to about 5000 nm. For the purposesof this invention, measurements refer only to the platelet particle andnot any dispersing aids or pretreatment compounds which might be used.

Preferably, the clays are dispersed in the polymer(s) so that most ofthe clay material exists as individual platelet particles, smalltactoids, and small aggregates of tactoids. Preferably, a majority ofthe tactoids and aggregates in the polymer-clay nanocomposites of thepresent invention will have thickness in its smallest dimension of lessthan about 20 nm. Polymer-clay nanocomposite compositions with thehigher concentration of individual platelet particles and fewer tactoidsor aggregates are preferred.

Moreover, the layered clay materials are typically swellable freeflowing powders having a cation exchange capacity from about 0.3 toabout 3.0 milliequivalents per gram of mineral (meq/g), preferably fromabout 0.90 to about 1.5 meq/g, and more preferably from about 0.95 toabout 1.25 meq/g. The clay may have a wide variety of exchangeablecations present in the galleries between the layers of the clay,including, but not limited to cations comprising the alkaline metals(group IA), the alkaline earth metals (group IIA), and their mixtures.The most preferred cation is sodium; however, any cation or combinationof cations may be used provided that most of the cations may beexchanged for organic cations. The exchange may occur by treating aindividual clay or a mixture of clays with organic cation or a mixtureof organic cations.

Preferred clay materials are phyllosilicates of the 2:1 type having acation exchange capacity of about 0.5 to about 2.0 meq/g. The mostpreferred clay materials are smectite clay minerals, particularly sodiumbentonite or sodium montmorillonite, more particularly Wyoming-typesodium montmorillonite or Wyoming-type sodium bentonite having a cationexchange capacity from about 0.95 to about 1.25 meq/g. The preferredclays have less than about 2.0 wt % of quartz, as measured by powderX-ray diffraction methods.

Other non-clay materials having the above-described ion-exchangecapacity and size, such as chalcogens, may also be used as a source ofplatelet particles under the present invention. Chalcogens are salts ofa heavy metal and group VIA (O, S, Se, and Te). These materials areknown in the art and do not need to be described in detail here.

Improvements in gas barrier result from increases in the concentrationof platelet particles in the polymer. While amounts of plateletparticles as low as about 0.01 percent provide improved barrier(especially when well dispersed and ordered), compositions having atleast about 0.5 weight percent of the platelet particles are preferredbecause they display the desired improvements in gas barrier.

Prior to incorporation into an oligomer(s) or polymer(s), the particlesize of the clay material may be reduced in size by methods known in theart, including, but not limited to, grinding, pulverizing, hammermilling, jet milling, and their combinations. It is preferred that theaverage particle size be reduced to less than about 100 micron indiameter, more preferably less than about 50 micron in diameter, andmost preferably less than about 20 micron in diameter.

The clay material of this invention may comprise refined or purified butunmodified clays, modified clays, or mixtures of modified and unmodifiedclays. Generally, it is desirable to treat the selected clay material tofacilitate separation of the agglomerates of platelet particles toindividual platelet particles and small tactoids. Separating theplatelet particles prior to incorporation into the polymer also improvesthe polymer/platelet interface. Any treatment that achieves the abovegoals may be used.

Many clay treatments used to modify the clay for the purpose ofimproving dispersion of clay materials are known and may be used in thepractice of this invention. The clay treatments may be conducted priorto, during, or after mixing the clay material with the polymer.

Organic Cations

In an embodiment of this invention, a pure, purified, modified ortreated layered clay material or mixture of clay material is prepared bythe reaction of a swellable layered clay(s) with an organic cation (toeffect partial or complete cation exchange), preferably an ammoniumcompound. If desired, two or more organic cations may be used to treatthe clay. Moreover, mixtures of organic cations may also be used toprepare a treated layered clay material. The process to prepare theorganoclays (modified or treated clays) may be conducted in a batch,semi-batch, or continuous manner.

Organic cations used to modify a clay material or a mixture of claymaterials of a nanocomposite of this invention are derived from organiccation salts, preferably onium salt compounds. Organic cation saltsuseful for the nanocomposite and process of this invention may generallybe represented by the following formula (I):

wherein M is either nitrogen or phosphorous; X⁻ is a halide, hydroxide,or acetate anion, preferably chloride and bromide; and R₁, R₂, R₃, andR₄ are independently organic and/or oligomeric ligands or may behydrogen.

Examples of useful organic ligands include, but are not limited tolinear or branched alkyl groups having 1 to 22 carbon atoms, aralkylgroups which are benzyl and substituted benzyl moieties includingfused-ring moieties having linear chains or branches of 1 to 100 carbonatoms in the alkyl portion of the structure, aryl groups such as phenyland substituted phenyl including fused-ring aromatic substituents, beta,gamma unsaturated groups having six or less carbon atoms, andalkyleneoxide groups having repeating units comprising 2 to 6 carbonatoms. Examples of useful oligomeric ligands include, but are notlimited to poly(alkylene oxide), polystyrene, polyacrylate,polycaprolactone, and the like.

Examples of useful organic cations include, but are not limited to alkylammonium ions, such as tetramethyl ammonium, hexyl ammonium, butylammonium, bis(2-hydroxyethyl) dimethyl ammonium, hexyl benzyl dimethylammonium, benzyl trimethyl ammonium, butyl benzyl dimethyl ammonium,tetrabutyl ammonium, di(2-hydroxyethyl) ammonium, and the like, andalkyl phosphonium ions such as tetrabutyl phosphonium, trioctyloctadecyl phosphonium, tetraoctyl phosphonium, octadecyl triphenylphosphonium, and the like or mixtures thereof.

Other particularly useful organic cations for this invention include,but are not limited to alkyl ammonium ions such as dodecyl ammonium,octadecyl trimethyl ammonium, bis(2-hydroxyethyl) octadecyl methylammonium, octadecyl benzyl dimethyl ammonium, and the like or mixturesthereof.

Useful alkoxylated ammonium compounds may include mono-alkoxylated,di-alkoxylated, tri-alkoxylated, and tetra-alkoxylated ammoniumcompounds. Examples of useful alkoxy ligands include, but are notlimited to hydroxyethyl, hydroxypropyl, hydroxybutyl, poly(ethyleneoxide), poly(propylene oxide), poly(butylene oxide), and the like.

Useful mono-alkoxylated ammonium salts can be represented as follows:

wherein N represents nitrogen; X⁻ represents an anion which ispreferably a halide atom such as chloride or bromide; R₁, R₂, and R₃ maybe the same or different and are selected from organic and oligomericligands comprising 1 to carbon atoms or may be hydrogen; n is at least1; R₄ is selected from hydrocarbons comprising 1 to 4 carbon atoms,hydrogen, and their mixtures; and R₅ is selected from hydrocarbonscomprising 1 to 7 carbon atoms and hydrogen. Illustrative of suitablemono-alkoxylated amine compounds, which are converted to the ammoniumsalt by reaction with a Bronsted acid, include, but are not limited tothose under the trade name of JEFFAMINE.

Useful di-alkoxylated ammonium salts can be represented as follows:

wherein N represents nitrogen; X⁻ represents an anion which ispreferably a halide atom such as chloride or bromide; R₁ and R₂ may bethe same or different and are selected from organic and oligomericligands comprising 1 to 30 carbon atoms or may be hydrogen; p and n areat least 1; and R₃, R₄, R₅ and R₆ may be same or different and areselected from hydrocarbons comprising 1 to 4 carbon atoms and hydrogen.Examples of useful di-alkoxylated ammonium compounds include, but arenot limited to bis(2-hydroxymethyl), octadecyl ammonium,bis(2-hydroxyethyl), octadecylmethyl ammonium,octadecylisopropoxydimethyl ammonium, and the like or mixtures thereof.

Useful tri-alkoxylated ammonium salts can be represented as follows:

wherein N represents nitrogen; X⁻ represents an anion which ispreferably a halide atom such as chloride or bromide; R₁ is selectedfrom organic and oligomeric ligands comprising 1 to 30 carbon atoms ormay be hydrogen; n, p, and q are at least 1; and R₂, R₃, R₄, R₅, R₆ andR₇ may be same or different and are selected from hydrocarbonscomprising 1 to 4 carbon atoms and hydrogen.

Useful tetra-alkoxylated ammonium salts can be represented as follows:

wherein N represents nitrogen; X⁻ represents an anion which ispreferably a halide atom such as chloride or bromide; m, n, p and q areat least 1; and R₁, R₂, R₃, R₄, R₅, R₆, R₇ and R₈ may be same ordifferent and are selected from hydrocarbons comprising 1 to 4 carbonatoms and hydrogen.

The preferred alkoxylated ammonium salts are di-ethoxylated ammoniumsalts represented as follows:

wherein N represents nitrogen; X⁻ represents an anion which ispreferably a halide atom such as chloride or bromide; R₁ is selectedfrom organic and oligomeric ligands comprising at least 8 carbon atoms;R₂ is selected from organic and oligomeric ligands comprising at least 8carbon atoms or may be hydrogen; and p and n are at least 1.

Illustrative examples of suitable polyalkoxylated ammonium compoundsinclude the hydrochloride salts of polyalkoxylated amines such asJEFFAMINE (of Huntsman Chemical), namely, JEFFAMINE-506 and JEFFAMINE505, and an amine available under the trade name ETHOMEEN (of AkzoChemie America), namely, ETHOMEEN 18/25, which is octadecylbis(polyoxyethylene[15])amine, wherein the numbers in brackets refer tothe total number of ethylene oxide units. A further illustrative exampleof a suitable polyalkoxylated ammonium compound is ETHOQUAD 18/25 (ofAkzo Chemie America), which is octadecyl methyl bis(polyoxyethylene[15])ammonium chloride, wherein the numbers in brackets refer to the totalnumber of ethylene oxide units.

Numerous methods to modify layered clays with organic cations are known,and any of these may be used in the practice of this invention. Oneembodiment of this invention is the organic modification of a layeredclay with an organic cation salt by the process of dispersing a layeredclay or mixture of clays into hot water, most preferably from about 50to about 80° C., adding (neat or dissolved in water or alcohol) theorganic cation salt or an organic amine and a Bronsted acid (therebyforming the organic ammonium salt in situ) separately or adding mixturesthereof with agitation, then blending for a period of time sufficientfor the organic cations to exchange most of the metal cations present inthe galleries between the layers of the clay material(s). Then, thepurified and organically-modified layered clay material(s) is isolatedby methods known in the art including, but not limited to, filtration,centrifugation, spray drying, and/or their combinations.

The particle size of the organoclay material may be reduced in size bymethods known in the art, including, but not limited to, grinding,pulverizing, hammer milling, jet milling, and/or their combinations. Itis preferred that the average particle size be reduced to less thanabout 100 micron in diameter, more preferably less than about 50 micronin diameter, and most preferably less than about 20 micron in diameter.It is important to remove large size particles, as they cause increasedhaze and voids.

It is desirable to use a sufficient amount of the organic cation salt(s)to permit exchange of most of the metal cations in the galleries of thelayered particle for the organic cation(s); therefore, at least about0.5 equivalent of total organic cation salt is used and up to about 3equivalents of organic cation salt can be used. It is preferred thatabout 0.5 to about 2 equivalents of organic cation salt be used, morepreferable about 1.0 to about 1.5 equivalents. It is preferable toremove most of the metal cation salt(s) and most of the excess organiccation salt(s) by washing and other techniques known in the art. Thepresence of the metal salts, such as sodium chloride, may lead toincreased haze and voids.

The organoclays of the present invention having reduced impurity may beincorporated into suitable matrix polymers such as polyamides by anyprocesses which are known in the art.

Other Clay Treatments

The layered clay material may be further treated for the purposes ofaiding exfoliation in the composite, increasing the molecular weightand/or improving the strength of the polymer/clay interface. Anytreatment that achieves the above goals may be used. Increasing themolecular weight of the polyamide-platelet particle composite may beachieved by several different methods including, but not limited to,reactive chain extension, solid state polymerization, crosslinking, andmelt compounding with a high molecular weight, melt processiblepolyamide.

Examples of useful treatments include, but are not limited tointercalation with water-soluble or water-insoluble polymers, organicreagents or monomers, silane compounds, metals or organometallics,expanding agents, oligomeric polymers, dispersing aids and/or theircombinations. Treatment of the clay can be accomplished prior to theaddition of a polymer to the clay material, during the dispersion of theclay with the polymer or during a subsequent melt blending or meltfabrication step.

Examples of useful pretreatment with polymers and oligomers includethose disclosed in U.S. Pat. Nos. 5,552,469 and 5,578,672, incorporatedherein by reference. Examples of useful polymers for treating the claymaterial include polyvinyl pyrrolidone, polyvinyl alcohol, polyethyleneglycol, polytetrahydrofuran, polystyrene, polycaprolactone, certainwater-dispersible polyesters, Nylon-6 and the like.

Examples of useful pretreatment with organic reagents and monomersinclude those disclosed in EP 780,340 A1, incorporated herein byreference. Examples of useful organic reagents and monomers forintercalating the swellable layered clay include dodecylpyrrolidone,caprolactone, caprolactam, ethylene carbonate, ethylene glycol,bishydroxyethyl terephthalate, dimethyl terephthalate, and the like ormixtures thereof.

Examples of useful pretreatment with silane compounds include thosetreatments disclosed in WO 93/11190, incorporated herein by reference.Examples of useful silane compounds includes(3-glycidoxypropyl)trimethoxysilane, 2-methoxy (polyethyleneoxy)propylheptamethyl trisiloxane, octadecyl dimethyl (3-trimethoxysilylpropyl)ammonium chloride and the like.

Examples of suitable water dispersible compounds include sulfonatedpolymers such as sulfonated polyesters and sulfonated polystyrene.

If desired, a dispersing aid may be present during or prior to theformation of the composite for the purposes of aiding exfoliation of thetreated or untreated swellable layered particles into the polymer. Manysuch dispersing aids are known and cover a wide range of materialsincluding water, alcohols, ketones, aldehydes, chlorinated solvents,hydrocarbon solvents, aromatic solvents, and the like or combinationsthereof.

It should be appreciated that on a total composition basis, dispersingaids and/or pretreatment compounds may account for significant amount ofthe total composition, in some cases up to about 30 weight percent.While it is preferred to use as little dispersing aid/pretreatmentcompound as possible, the amounts of dispersing aids and/or pretreatmentcompounds may be as much as about 9 times the amount of the plateletparticles.

Articles

The polymer-clay nanocomposite of this invention may be formed intoarticles by conventional plastic processing techniques. Molded articlesmay be made from the above-described polymers by compression molding,blow molding, extrusion or other such molding techniques, all of whichare known in the art. Monolayer and/or multilayer articles prepared fromthe nanocomposite material of this invention include, but are notlimited to film, sheet, pipes, tubes, profiles, molded articles,preforms, stretch blow molded films and containers, injection blowmolded containers, extrusion blow molded films and containers,thermofomied articles and the like. The containers are preferablybottles.

Oriented articles produced from the present polymer-clay compositionsare also expected to have low haze and reduced voids. Compositecompositions produced according to the present invention are especiallyuseful for preparing clear bottles and film (low haze) that may alsoexhibit improved gas barrier properties. Additionally, products producedfrom these composites can achieve lower haze and possibly higher gasbarrier properties than products produced from conventional polymer-claycomposites.

In forming stretch blow molded bottles of one or several layers, it isoften customary to initially form a preform of the desired vessel via aninjection molding process. The crystallization rate of the materialscomprising the preform must be sufficiently slow to allow the formationof an essentially noncrystalline article. Unless the preform isessentially noncrystalline, it is exceedingly difficult to stretch blowmold into the desired shape to form a bottle. In one embodiment of thisinvention, the layered silicate materials and treatment compounds areselected both to promote dispersion of the individual platelets into thepolymer, e.g., polyamide to allow maximum barrier enhancement, minimumhaze formation, and the formation of preforms by injection molding whichare essentially noncrystalline in character.

The bottles and containers of this invention provide increased shelfstorage life for contents, including beverages and food that aresensitive to the permeation of gases. Articles, more preferablycontainers, of the present invention often display a gas transmission orpermeability rate (oxygen, carbon dioxide, water vapor) which is atleast about 10% lower (depending on clay concentration) than that ofsimilar containers made from clay-free polymer, resulting incorrespondingly longer product shelf life provided by the container.Desirable values for the sidewall modulus and tensile strength may alsobe maintained. The articles also show unexpected resistance to hazeformation, crystallization, void and other defect formation.

The articles may also be multilayered. Preferably, the multilayeredarticles have a nanocomposite material disposed between other layers,although the nanocomposite may also be one layer of a two-layeredarticle. In embodiments where the nanocomposite and its components areapproved for food contact, the nanocomposite may form the food contactlayer of the desired articles. In other embodiments, it is preferredthat the nanocomposite be in a layer other than the food contact layer.

The multilayer articles may also contain one or more layers of thenanocomposite composition of this invention and one or more layers of astructural polymer. A wide variety of structural polymers may be used.Illustrative of structural polymers are polyesters, polyetheresters,polyamides, polyesteramides, polyurethanes, polyimides, polyetherimides,polyureas, polyamideimides, polyphenyleneoxides, phenoxy resins, epoxyresins, polyolefins, polyacrylates, polystyrene, polyethylene-co-vinylalcohols (EVOH), and the like or their combinations and blends. Thepreferred structural polymers are polyesters, such as poly(ethyleneterephthalate) and its copolymers.

In another embodiment, co-extruding a layer of the polymer-claynanocomposite specified above with some other suitable thermoplasticresin may form articles. The polymer-clay nanocomposite and the moldedarticle and/or extruded sheet may also be formed at the same time byco-injection molding or co-extruding.

Another embodiment of this invention is the combined use of silicatelayers uniformly dispersed in the matrix of a high barrier thermoplastictogether with the multilayer approach to packaging materials. By using alayered clay to decrease the gas permeability in the high barrier layer,the amount of this material that is needed to generate a specificbarrier level in the end application is greatly reduced.

Since the high barrier material is often the most expensive component inmultilayer packaging, a reduction in the amount of this material usedcan be quite beneficial. With the polymer-clay nanocomposite layer beingsandwiched between two outer polymer layers, the surface roughness isoften considerably less than for a monolayer nanocomposite material.Thus, with a multilayer approach, the level of haze may be furtherreduced.

Nanocomposite Processes

The polymer-clay nanocomposites of this invention may be prepared withthe matrix polymer and layered clay material in different ways. Manyprocesses to prepare polymer-clay nanocomposite compositions are known,and any of these processes may be used to prepare the composites of thispresent invention.

In one embodiment of this invention, the melt mixing step is achieved bydry mixing polymer with a layered clay having a low quartz content andpassing the mixture through a compounding extruder under conditionssufficient to melt the polymer.

In another embodiment of this invention, the melt-mixing step isconducted by feeding the polymer and treated or untreated layeredparticles separately into a compounding extruder. When treated layeredparticles are used in this process, it is usually preferred that thepolymer be added first to minimize degradation of treated layeredparticles.

This invention also relates generally to a process comprising the stepsof (1) preparing an oligomeric resin-platelet particle composite by meltmixing a low quartz clay material comprising platelet particles and anoligomeric resin and (2) preparing a high molecular weight polymer-claynanocomposite material.

In a one embodiment of this process, the steps comprise: (i) melt mixingplatelet particles with a matrix polymer-compatible oligomeric resin toform an oligomeric resin-clay composite, and (ii) mixing the oligomericresin-clay composite with a high molecular weight matrix polymer therebyincreasing the molecular weight of the oligomeric resin-plateletparticle composite and producing a polymer nanocomposite material.

In another embodiment of the first embodiment, the melt-mixing step isconducted by feeding the oligomeric resin and treated or untreatedlayered particles separately into a compounding extruder. When treatedlayered particles are used in this process, it is preferred that theoligomeric resin be added first to minimize degradation of treatedlayered particles.

Melt processing or mixing includes melt and extrusion compounding. Useof extrusion compounding to mix the clay and the polymer presents twoadvantages. Chiefly, the extruder is able to handle the high viscosityexhibited by the nanocomposite material. In addition, in a melt mixingapproach for producing nanocomposite materials, the use of solvents canbe avoided. Low molecular weight liquids can often be costly to removefrom the nanocomposite resin. Moreover, use of extrusion compounding tomix the clay and the polymer is preferred because of the ease ofpreparation and the potential to attain high clay loadings.

In another embodiment of this invention, a high concentration of layeredparticles is melt mixed with oligomeric resin by mixing in a reactor.The resulting composite material is then either chain extended,polymerized to high molecular weight, or let down in the extruder into ahigh molecular weight polymer to obtain the final nanocompositematerial.

The oligomeric resin and the high molecular weight polymer may have thesame or different repeat unit structure, i.e., may be comprised of thesame or different monomer units. Preferably, the oligomeric resin hasthe same monomer unit to enhance compatibility or miscibility with thehigh molecular weight polymer.

In another embodiment of this invention, molten oligomeric resin may befed directly to a compounding extruder along with treated or untreatedlayered particles to produce the oligomeric resin-platelet particlenanocomposite.

If desired, a dispersing aid may be present during or prior to theformation of the composite by melt mixing for the purposes of aidingexfoliation of the treated or untreated swellable layered particles intothe polymer. Many such dispersing aids are known covering a wide rangeof materials including water, alcohols, ketones, aldehydes, chlorinatedsolvents, hydrocarbon solvents, aromatic solvents, and the like orcombinations thereof.

The molecular weight of the polymer material may be increased by any ofa number of known approaches or by any combination of these approaches,e.g., chain extension, reactive extrusion, extrusion let-down, solidstate polymerization or annealing, annealing under a flow of inert gas,vacuum annealing, let-down in a melt reactor, etc.

Although any melt mixing device may be used, typically, melt mixing isconducted either by a batch mixing process or by a melt compoundingextrusion process during which treated or untreated layered clayparticles are introduced into an oligomeric or polymeric resin. Prior tomelt mixing, the treated or untreated layered particles may exist invarious forms including pellets, flakes, chips and powder. It ispreferred that the treated or untreated layered particles be reduced insize by methods known in the art, such as hammer milling and jetmilling. Prior to melt mixing, the oligomeric or polymeric resin mayexist in wide variety of forms including pellets, ground chips, powderor its molten state.

As exemplified above, the layered clay having a low quartz content andthe matrix polymer components of the nanocomposite of this invention maybe combined in a wide variety of ways that are known to those skilled inthe art. Therefore, it will be apparent to those skilled in the art thatvarious modifications and variations can be made to the processesembodied above without departing from the scope of the invention. Otherembodiments of the invention will be apparent to those skilled in theart from consideration of the specification and practice of theinvention disclosed herein. It is intended that the description of theabove embodiments not be limiting.

The resulting nanocomposite can then be processed into the desiredbarrier article, film or container with article-forming methods wellknown in the art. For example, the nanocomposite may then be processedeither as an injected molded article, e.g., a container preform or anextruded film or sheet. Additional processing of stretch blow molding toa container or bottle, or extruding as a barrier film yields highbarrier finished articles with low haze and reduced voids. Polymernanocomposites and articles produced according to the present inventiondisplay a gas permeability, which is at least 10 percent lower than thatof the unmodified polymer.

EXAMPLES

The following examples and experimental results are included to providethose of ordinary skill in the art with a complete disclosure anddescription of particular manners in which the present invention can bepracticed and evaluated, and are intended to be purely exemplary of theinvention and are not intended to limit the scope of what the inventorsregard as their invention. Efforts have been made to ensure accuracywith respect to numbers (e.g., amounts, temperature, etc.); however,some errors and deviations may have occurred. Unless indicatedotherwise, parts are parts by weight, temperature is in ° C. or is atambient temperature, and pressure is at or near atmospheric.

Example 1

Example 1 illustrates one embodiment of a nanocomposite of the presentinvention.

MXD6 6007, poly(m-xylylene adipamide) with an I.V. of about 1.1 dL/g,was purchased from Mitsubishi Chemical Co. The organo-montmorilloniteclay (PGC-Q182) was provided by Nanocor Inc. of Arlington Heights, Ill.The clay has a quartz content of 0.33 wt % determined from X-raydiffraction method. Also, this organoclay has a Na⁺ content of 0.12 wt%, as determined by X-ray diffraction.

The organo-montmorillonite clay was prepared by onium ion exchangingNa-montmorillonite with bis(2-hydroxyethyl) octadecyl methyl ammoniumchloride. The finished product was washed with alcohol/water mixture toremove excess surfactant then dried and milled. The tether on the clayis bis(2-hydroxyethyl) octadecyl methyl ammonium.

D(ND), a low molecular weight m-xylyladipamide polyamide was purchasedfrom Polymer Chemistry Innovations. This material was analyzed bytitration of the amine and carboxylate end groups to possess a numberaverage molecular weight of about 3,000, and was determined to have anLV. of about 0.41 dL/g. 1421.8 grams of this oligomericpoly(m-xylyladipoyl diamine) was dry mixed with 378.2 grams oforganomontmorillonite clay from Nanocor, Inc. Prior to dry mixing, theindividual components were dried at 80C. under vacuum for 24 hours. Themixture was then extruded on the Leistritz Micro 18 co-rotating twinscrew extruder equipped with a general compounding screw. The AccuRatepellet feeder was set at a rate of approximately 2 kg/hr with a nitrogenatmosphere over both the feeder and the hopper. The barrel and dietemperatures were set at 240C. and the screw RPM at approximately 200.

After the extrusion was complete, 1666.7 grams of the extrudate pelletsare dry-mixed with 8333.3 grams of MXD6 6007 polyamide. The mixture wasthen extruded on the Werner-Pflider 30 mm twin screw extruder at aprocessing temperature of 260C. and a screw RPM of 300 at a feed rate ofabout 30 lb/hr. The final material was analyzed for ash content and itwas determined to be 2.53%.

The resulting nanocomposite material, designated asMXD6/D(ND)/organoclay 2.53%, was used as the middle layer of co-injectedtrilayer preforms. The ash content of the resulting nanocomposite was2.53%. The inner and outer layers of the trilayer preform were made fromEastman's amber colored PET 20261, having about 0.80 dL/g I.V. Thenominal thickness of the middle layer was about 8% of the totalthickness. The preforms were stretch blow molded on Sidel SBO ⅔ machineinto 16 oz. beer bottle. The bottle sidewall was cut and the middlelayer containing the nanocomposite material was peeled from thethree-layer configuration, and analyzed for haze, oxygen permeabilityand optical microscopy. The haze of the middle layer was 8%. The hazewas determined by ASTM test method D-1003. The middle layer was alsosubjected to optical microscopy and relatively fewer voids were observedas compared to the film of Comparative Example 2 (See FIGS. 2 and 3).

Examples 2a-2e and Comparative Example 1f

Examples 2a-2e illustrate various embodiments of the present invention.Example 1f is a comparative example. Example 2g is a control samplehaving only MXD6 in the middle layer.

MXD6 6007, poly(m-xylylene adipamide) with an I.V. of about 1.1 dL/g,was purchased from Mitsubishi Chemical Co. The organo-montmorilloniteclays (Nanomer types) were provided by Nanocor Inc. of ArlingtonHeights, Ill. The quartz content of the clay is shown in Table 2.

The montmorillonite clays were purified by the process described intheir U.S. Pat. No. 6,050,509, and the organo-montmorillonite clay wassupplied by Nanocor, Inc., Arlington Heights, Ill. The modifiedmontmorillonite clay was washed extensively until free of non-exchangedsurfactant, and then dried and milled. D(ND), a low molecular weightm-xylyladipamide polyamide was purchased from Polymer ChemistryInnovations. This material was analyzed by titration of the amine andcarboxylate end groups to possess a number average molecular weight ofabout 3,000 g/mol, and was determined to have an I.V. of about 0.41dL/g. 21.1% by weight of the oligomeric poly(m-xylyladipoyl diamine),3.9% of organo-montmorillonite from Nanocor, Inc. and 75% by wt. ofMXD6-6007 from Mitsubishi Chemical Co. were then extruded on the 57 mmtwin screw extruder equipped with a general compounding screw. Thebarrel and die temperatures were set at about 270° C.

The final materials were analyzed for ash content and are listed inTable 2.

The resulting nanocomposite materials, (Examples 2a-2e and ComparativeExample 1f), were used as the middle layer of co-injected trilayerpreforms. Sample 2g (no clay) was prepared using MXD6-6007 in the middlelayer. The inner and outer layers of the trilayer preform were made fromEastman Chemical Company PET 9921W, having about 0.80 dL/g I.V. Thenominal thickness of the middle layer was about 10% of the totalthickness. The preforms were stretch blow molded on a Sidel SBO ⅔machine into 16 oz. bottle. The bottle sidewall was cut and the middlelayer containing the nanocomposite material for samples 2a through 2e,Comparative Example 1f, and M6-6007 for sample 2g was peeled from thethree-layer configuration, and analyzed for haze and oxygenpermeability.

The oxygen barrier of the film was then determined by ASTM test methodD-3985 at 30° C. and 50% relative humidity with a pure oxygen gaspermeant and a nitrogen gas carrier on a Mocon 2/20 oxygen permeabilitytester. The oxygen permeability of the middle layer containing thenanocomposite was at least 20% lower for samples 2a-2e and ComparativeExample 1f than for sample 2g. The haze of the middle layer is shown inTable 2. The haze was determined by ASTM test method D-1003. As shown inTable 2, as the quartz weight percent decreases, the haze decreases.Moreover, the middle layer was also subjected to optical microscopy andrelatively fewer voids were observed in samples 2a, 2b, 2c, 2d and 2e,compared to sample 1f, a comparative example.

TABLE 2 Middle Layer Middle Quartz Thickness Layer NanomerType Wt. (%)Ash (%) (mils) Haze Example 2a NA-047-00 0.33 2.2 1.63 8.6 2b NX-041-00A0.55 2.1 1.68 8.1 2c NX-039-00A 0.79 2.6 1.58 12.4 2d NV-049-00 1.58 21.8 13.9 2e NN-049-00 1.93 2.1 1.8 14.8 Comparative NN-195-99 3.7 2.51.7 23 Example 1f 2g None 0 0 1.7 0.9

Example 3

Example 3 illustrates one embodiment of a nanocomposite of the presentinvention.

MXD6 6007, poly(m-xylylene adipamide) with an I.V. of about 1.1 dL/g,was purchased from Mitsubishi Chemical. The super clean or purifiedorgano-montmorillonite clay (S-PGW-ODA) was provided by Nanocor Inc. ofArlington Heights, Ill. This clay was produced by using the super-cleanprocess of the present invention.

That is, S-PGW-ODA was prepared by using cryogenic magnetically purifiedoctadecyl ammonium-montmorillonite clay (Nanocor, Inc., ArlingtonHeights, Ill.). Protonated octadecyl ammonium (ODA) up to excess of 100%of the clay PGW was used to exchange the inorganic Na⁺ or Ca²⁺ out. Themodified montmorillonite clay was washed extensively until free ofnon-exchanged surfactant, and then dried and milled. The tether on theclay is octadecyl ammonium. 100% of the PGW was utilized. D(ND), a lowmolecular weight m-xylyladipamide polyamide was purchased from PolymerChemistry Innovations. This material was analyzed by titration of theamine and carboxylate end groups to possess a number average molecularweight of about 3,000, and was determined to have an I.V. of about 0.41dL/g. 1421.8 grams of this oligomeric poly(m-xylyladipoyl diamine) wasdry mixed with 378.2 grams of S-PGW-ODA organo-montmorillonite clay fromNanocor, Inc. Prior to dry mixing, the individual components were driedat 80° C. under vacuum for 24 hours. The mixture was then extruded onthe Leistritz Micro 18 co-rotating twin screw extruder equipped with ageneral compounding screw. The AccuRate pellet feeder was set at a rateof approximately 2 kg/hr with a nitrogen atmosphere over both the feederand the hopper. The barrel and die temperatures were set at 240° C. andthe screw RPM at approximately 200.

After the extrusion was complete, 1666.7 grams of the extrudate pelletsare dry-mixed with 8333.3 grams of MXD6 6007 polyamide. The mixture wasthen extruded on the Werner-Pfleider 30 mm twin screw extruder at aprocessing temperature of 260° C. and a screw RPM of 300 at a feed rateof about 30 lb/hr. The final material was analyzed for ash content andit was determined to be 2.53%.

The resulting nanocomposite material, designated as MXD6/D(ND)/S-PGW-ODA2.53%, was used as the middle layer of co-injected trilayer preforms.The ash content of the resulting nanocomposite was 2.53%. The inner andouter layers of the trilayer preform were made from Eastman's ambercolored PET 20261, having about 0.80 dL/g I.V. The nominal thickness ofthe middle layer was about 8% of the total thickness. The preforms werestretch blow molded on Sidel SBO ⅔ machine into 16 oz. beer bottle. Thebottle sidewall was cut and the middle layer containing thenanocomposite material was peeled from the three-layer configuration,and analyzed for haze, oxygen permeability and optical microscopy.

The oxygen barrier of the film was then determined by ASTM test methodD-3985 at 30° C. and 50% relative humidity with a pure oxygen gaspermeant and a nitrogen gas carrier on a Mocon 2/20 oxygen permeabilitytester to be 0.13 cc mil/100 in²-24 hr.-atm. The haze of the middlelayer was 11.1%. The haze was determined by ASTM test method D-1003. Themiddle layer was also subjected to optical microscopy and relativelyfewer voids were observed as compared to the film of Comparative Example2 (See FIGS. 2 and 3.)

Comparative Example 2

In this example, instead of using super clean or purified S-PGW-ODAclay, the clay was prepared via regular process (FIG. 1) and isdesignated as only, type PGW-ODA. The procedure of Example 3 of theinvention was essentially repeated. MXD6 6007, poly(m-xylyleneadipamide) with I.V. of about 1.1 dL/g was purchased from MitsubishiChemical. The regular non-purified PGW-ODA organo-montmorillonite claywas provided by Nanocor, Inc. of Arlington Heights, Ill. This clay wasproduced by using a conventional process. Standard PGW-ODA was preparedby using purified Na-montmorillonite clay (Nanocor, Inc., ArlingtonHeights, Ill.). Protonated octadecyl ammonium (ODA) up to excess of 25%of the PGW clay was used to exchange the inorganic Na⁺ or Ca²⁺ cations.The modified montmorillonite clay was washed extensively until free ofnon-exchanged surfactant, and then dried and milled. The tether on theclay is octadecyl ammonium. 100% of the PGW was utilized.

D(ND), a low molecular weight m-xylyladipamide polyamide was purchasedfrom Polymer Chemistry Innovations. This material was analyzed bytitration of the amine and carboxylate end groups to possess a numberaverage molecular weight of about 3,000, and was determined to have anI.V. of about 0.41 dL/g. 4734.6 grams of this oligomericpoly(m-xylyladipoyl diamine) was dry mixed with 1265.38 grams of PGW-ODAorgano-montmorillonite clay from Nanocor, Inc. Prior to dry mixing, theindividual components were dried at 80° C. under vacuum for 24 hours.The mixture was then extruded on the Leistritz Micro 18 co-rotating twinscrew extruder equipped with a general compounding screw. The AccuRatepellet feeder was set at a rate of approximately 2 kg/hr with a nitrogenatmosphere over both the feeder and the hopper. The barrel and dietemperatures were set at 240° C. and the screw RPM at approximately 200.

After the extrusion was complete, 1666.7 grams of the extrudate pelletsare dry-mixed with 8333.3 grams of M6 6007 polyamide. The mixture wasthen extruded on the Werner-Pfleider 30 mm twin screw extruder at aprocessing temperature of 260° C. and a screw RPM of 300 at a feed rateof about 30 lb/hr. The final material was analyzed for ash content andit was determined to be 2.41%.

The resulting nanocomposite material, designated as MXD6/D(ND)/PGW-ODA2.41%, was used as the middle layer of co-injected trilayer preforms.The ash content of the resulting nanocomposite was 2.41%. The inner andouter layers of the trilayer preform were made from Eastman's ambercolored PET 20261, having about 0.80 dL/g I.V. The nominal thickness ofthe middle layer was about 8% of the total thickness. The preforms werestretch blow molded on Sidel SBO ⅔ machine into 16 oz. bottles. Thebottle sidewall was cut and the middle layer containing thenanocomposite material was peeled from the three-layer configuration,and analyzed for haze, oxygen permeability and optical microscopy.

The oxygen barrier of the film was then determined by ASTM test methodD-3985 at 30° C. and 50% relative humidity with a pure oxygen gaspermeant and a nitrogen gas carrier on a Mocon 2/20 oxygen permeabilitytester to be 0.15 cc mil/100 in²-24 hr.-atm. The haze of the middlelayer was 15.8%. The haze was determined by ASTM test method D-1003. Themiddle layer was also subjected to optical microscopy (see FIG. 3) andrelatively more voids were observed as compared to the film of Example 3(See FIGS. 2 and 3).

The resulting nanocomposite material was also extruded into tri-layerfilms with Eastman's PET (of Eastman Chemical Company, Kingsport, Tenn.)as outside layers. The thickness of the nanocomposite is about 10percent. Optical micrographs were taken on the tri-layer films up to400× magnification. Dark particles were observed (FIG. 4A, and 4B).Then, the tri-layer film was biaxially stretched 4×4 at about 100° C. ina T. M. Long instrument. Micrographs were taken at the same locationclose to the dark particles. The dark particles either disintegrated, asshown in FIG. 5A, or remained unchanged, as shown in FIG. 5B. In bothcases, there are significant hollow rings associated with the particles.

Throughout this application, various publications are referenced. Thedisclosures of these publications in their entireties are herebyincorporated by reference into this application in order to more fullydescribe the state of the art to which this invention pertains.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the scope or spirit of the invention. Otherembodiments of the invention will be apparent to those skilled in theart from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. An intercalate comprising a layered clay materialhaving less than about 2.0% by weight of quartz, based on the weight ofthe clay material, intercalated with an organic cation intercalant and apolyamide oligomer or polymer intercalant selected from the groupconsisting of poly (m-xylylene adipamide); a copolymer thereof; nylon 6;nylon 6,6; and a mixture thereof.
 2. The intercalate of claim 1, whereinthe layered clay material comprises montmorillonite, hectorite, mica,vermiculite, bentonite, nontronite, beidellite, volkonskoite, saponite,magadite, kenyaite, or a mixture thereof.
 3. The intercalate of claim 1,wherein the clay material comprises sodium montmorillonite or sodiumbentonite.
 4. The intercalate of claim 1, wherein the layered claymaterial has less than about 1.0% by weight of quartz particles.
 5. Theintercalate of claim 1, wherein the organic cation intercalant isderived from an ammonium salt compound.
 6. The intercalate of claim 1,wherein the polyamide oligomer or polymer intercalant comprisespoly(m-xylylene adipamide) or a copolymer thereof, and the clay materialcomprises sodium montmorillonite or sodium bentonite.
 7. The intercalateof claim 1 that functions to decrease the gas permeability and haze ofthe polyamide intercalant.
 8. The intercalate of claim 7, wherein thepolyamide comprises poly(m-xylylene adipamide) or a copolymer thereof,and the clay material comprises sodium montmorillonite or sodiumbentonite.
 9. The intercalate of claim 4, wherein the layered claymaterial has less than about 0.7% by weight quartz.
 10. The intercalateof claim 9, wherein the layered clay material has less than about 0.5%by weight quartz.
 11. A process for preparing an intercalate comprisingthe steps of: (i) intercalating a layered clay material with an organiccation, wherein the layered clay material has less than about 2.0% byweight of quartz, based on the weight of the layered clay material; and(ii) further intercalating the layered clay material with a melt of apolyamide oligomer or polymer intercalant selected from the groupconsisting of poly (m-xylylene adipamide); a copolymer thereof; nylon 6;nylon 6,6; and a mixture thereof.
 12. The process of claim 11, whereinsteps (i) and (ii) are conducted by a batch mixing or a melt compoundingextrusion process.
 13. The process of claim 11, wherein the layered claymaterial has less than about 0.7% by weight quartz.
 14. The process ofclaim 13, wherein the layered clay material has less than about 0.5% byweight quartz.
 15. The process of claim 13 wherein the polyamideoligomer or polymer intercalant comprises poly(m-xylylene adipamide), acopolymer thereof, or a mixture thereof.
 16. The process of claim 11,wherein the polyamide oligomer or polymer intercalant comprisespoly(m-xylylene adipamide), a copolymer thereof, or a mixture thereof.17. The process of claim 13 that functions to decrease the gaspermeability and haze of the polyamide intercalant.
 18. The process ofclaim 14 that functions to decrease the gas permeability and haze of thepolyamide intercalant.